In carrying out power amplification, a power amplifier normally utilizes nonlinear elements such as transistors, diodes, and other nonlinear semiconductor devices. As a result, a nonlinear distortion may occur in an output signal of the power amplifier. For instance, as the magnitude of an input signal increases, the ratio between the magnitude of the output signal and that of the input signal, i.e., a gain of the power amplifier, may become irregular. This phenomenon is known as amplitude modulation-amplitude modulation distortion (hereinafter referred to as AM-AM distortion). Similarly, as the magnitude of an input signal increases, a phase shift of the output signal may also occur. This phenomenon is known as amplitude modulation-phase modulation distortion (hereinafter referred to as AM-PM distortion). Such distortions may deteriorate the reliability of the output signal, and the efficiency of the power amplifier.
In order to compensate for the AM-PM distortion and the AM-AM distortion, various linearization schemes have been used, but with limited success as the effect of linearization tends to decrease as the bandwidth of a signal increases.
Accordingly, there has existed a need for a power amplifier capable of preventing nonlinear distortion over a wide range of bandwidth.